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Advice on how to build a natural stone vented heat shield?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by The Dude, Feb 5, 2011.

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  1. The Dude

    The Dude New Member

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    Hi Folks,

    I am getting ready to build the hearth for my wood stove right now. I'm set on using natural stone collected from a nearby creekbed to face the non-combustible heat shield wall. I thought I'd be able to use Durock spaced an inch from the existing finished drywall, drilled into the studs behind the drywall with a lot of 3-1/2 screws, and then on the face of the Durock apply mortar and the creek stone, face-on. By face-on, I mean applying it like up on it's side you would veneer rather than how you'd stack stone to build outdoor landscape wall.

    Someone mentioned to me yesterday that this can't be done with natural stone for several reasons, and the reasons scared me, but I wonder if he is just biased from his own use of manufactured stone. His reasons that my plan would not work are:

    1.) Natural stone is so heavy that the floor below might not support it
    2.) The stones will not stay in place when trying to set them
    3.) The Durock and studs in the wall are not adequate support for hanging such weight onto the face of the Durock.

    I am having a heck of a tme finding any information that supports or refutes my plan. I can't find anything about building a natural stone hearth as a vented heath shield for a wood stove. Can anyone help?

    Some specs/plans for my situation:
    -Harman TL-300 wood stove
    -Position of stove is just under combustible clearance, so non-combustible is required.
    -Stone-faced heat shield for walls planned to top off at about 5 ft. high once clearance to combustibles is met (not going all the way up to ceiling)
    -Hearth will have a slate tile floor flush with bordering carpet and a raised pad for stove
    -Stone I plan to gather will hopefully be thin sandstone or maybe shale, averaging 1" thickness if possible. I may also look into splitting the stone for a flat side adhered against wall. I know some of the sandstone I find when fishing splits flat pretty easily.
    -I have no masonry experience, but a degree in sculpture and pretty good DYI knowledge and confidence. I research stuff to death and take a long time on projects to do them right.

    Thanks!
    Tom

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  2. begreen

    begreen Mooderator Staff Member

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    Sounds like it will work ok. There have been several stone veneer back walls posted here. Use long, doubled-up, 3" strips of 1/2" durock, on each stud, to create the 1" spacers. Screw the durock every 6-8" and it will be very solid. You can carry the stone down to the hearth at the stud point for greater support, but the wall will hold it. Just keep a 1" slot open between the studs at top and bottom to allow good ventilation.

    Here's a helpful video in 2 parts: http://www.youtube.com/watch?v=caIrspofCNo

    There are also several threads here where folks have done their own work. Hopefully some of them will chime in here and help you out.

    http://www.hearth.com/econtent/index.php/forums/viewthread/61709/
    http://www.hearth.com/econtent/index.php/forums/viewthread/58712/P22/
  3. jimbom

    jimbom Combustion Analyzer

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    Might check the structure. The stove will weigh 500 - 600 pounds. Concrete, mortar, and stone can be approximated at 150 pounds/ft^3. Depending on your installation you might be adding ~ 1000+ pounds to your floor dead load. If the floor structure will carry this, you should be good to go.
  4. southbalto

    southbalto Feeling the Heat

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    I took on a similar project using bluestone (about an 1" in thickness).

    No issues so far.

    I had a stihl cut off saw....big diamond blade. It was a must for getting the stone to the correct thickness. I imagine you could rent one from HD for the day. I used sakrete <s> pre mix stone veneer mortar.

    Here's the link: http://www.hearth.com/econtent/index.php/forums/viewthread/65623/

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  5. southbalto

    southbalto Feeling the Heat

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    YOu're probably well aware, but be sure to moisten the durarock before you apply the stone. It will really help it adhere.
  6. Highbeam

    Highbeam Minister of Fire

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    Plain dirt weighs more than 150lbs per cubic foot. The wall will be bearing the weight of the stone veneer so long as you adequately attach the durock. Is that wall an outside wall setting on the foundation or an internal wall supported by the interior floor system? I wouldn't think twice about your plan on an exterior wall. How big of stones are you talking about. Round creek stones in my area can be the size of golf balls or the size of basketballs, if you choose basketballs then the weight is much much higher per SF of wall than if you choose golfballs. If you use golfballs then I think it will look very busy like a pea gravel wall.

    I'm all for a different approach so please post pics.

    Good job plumbing in the OAK southbalto. I have a similar setup with no veneer... yet.
  7. The Dude

    The Dude New Member

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    Thank you so much for the helpful responses.

    Southbalto, I did not know to moisten the Durock first, so thank you for the excellent tip. Now I'm wondering if there;s something else "obvious" that I do not know. Is lath needed to adhere the mortar, or will it stick directly to the Durock?

    Highbeam, The stove will be in a corner with the heat shield wall on two sides. The rear is an exterior wall, and the other wall is load bearing. I will take pictures eventually, but for now I'll try to explain the load bearing wall. It supports the joists for the second floor, and the joists below it are supported by a steel I-beam in the basement ceiling that parallels the load bearing wall almost directly below. I think I am okay for support of the weight, although that is an assumption and might be a terrible thing to be wrong about.

    I am going out to gather stone tomorrow if it's not too frozen, which should be fun.

    I am excited about this hearth. Natural slate tile floor (unfortunately imported from India and not local), raised pad for stove (thanks for forum advice), natural stone wall surround from gathered local creek stone, all bordered by figured quarter-sawn white oak, craftsman style. And I plan to build a mantel on top of the stone wall also with quarter sawn oak. Hopefully I'll actually get one or two burns in before things warm up.
  8. southbalto

    southbalto Feeling the Heat

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    Lath isn't necessary. Just make sure the durarock is firmly attached to the wall and you moisten with a spray bottle.

    That Sackrete <s> stone veneer mortar worked well for me.

    You might also consider thinset to secure the stone to the wall. When I was doing my research I found a couple masonry/home improvement forums in which members reported good success with it. One poster indicated that once set in thinset it was virtually impossible to separate the rock from the durarock. Apparently, the facing of the durarock would break away before the rock seperated from the board.
  9. southbalto

    southbalto Feeling the Heat

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    Take a bunch of photos and put them up here.

    looking forward to seeing the final project
  10. begreen

    begreen Mooderator Staff Member

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    Sounds like it is going to look very nice. Gather a lot more stone than you think you will need so that you have lots of choices as it goes together. Let the stone come up to ambient temperature before using. And keep in mind the minimum clearance requirements for the wood trim and mantel from the connector pipe. 18" for single-wall, 6" for double-wall.
  11. Hogwildz

    Hogwildz Minister of Fire

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    Guys, he is taking about real stone, not veneer. If your going to be trying to hang river rock or field stone, I agree with the weight & stability issues represented to you.
    Real will be MUCH heavier than veneer. And will not stick to durock.
    Unless the stone you are thinking of using is very thin in thickness.
    True stone walls are started on a ledge or foundation strong enough to to support the serious weight a stone wall would present. I highly doubt you have that support under where you plan setting that wall.
    If I am reading this correctly, I agree with the advise first given to you. Hate to be a nay sayer, but real stone & veneer are two different beasts, with two different installation procedures & requirements.
    Research well before you commit. Talk to some stone masons.
  12. The Dude

    The Dude New Member

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    The rear face of the connector pipe is 14" from the combustible dry wall, so I will be using single wall stove pipe with a heat shield on the backside of it. I forget what the chimney guy said that reduces the clearance to. Is it 66% reduction (18" down to 6"), or is it less of a reduction? If I make my mantel 8" out from the wall, that would bring the clearance to 6".
  13. begreen

    begreen Mooderator Staff Member

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    Sounds veneer-like to me Hog, but perhaps I am misunderstanding.

    With the pipe heat shield the clearance will be 6" minimum.
  14. southbalto

    southbalto Feeling the Heat

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    Yea I cut my bluestone down to about 1/2"-3/4" thickness. No issues so far.

    One other important step. If you're using a saw to reduce the thickness, cut a few grooves in the stone on the side being adhered to the wall. It will give the mortar something to grab onto.
  15. Hogwildz

    Hogwildz Minister of Fire

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    Good points. If cutting thinner as you did, he should be able to do this. But, you did not go floor to ceiling. That would effectively at minimal double the weight load on the same foundation area.
    Not sure it that would be overload or not? If he is doing similar to what you did, he may be ok. But if he is trying to use field stone or larger river rock, may be a different story.
    How did you reduce the thickness of your stone? I assume they were all short enough to get a saw blade through.
    Excellent point on creating grooves in back for the mortar to grab.
  16. southbalto

    southbalto Feeling the Heat

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    stihl ts400 cut off saw

    must have for a project like this
  17. Highbeam

    Highbeam Minister of Fire

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    I agree with you hogz, that's why I pointed out the difference between basketball sized rock and golfball sized rock. Taken to the extreme he could make it out of pea gravel for an exposed aggregate look wall. We don't know.
  18. madison

    madison Minister of Fire

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    I watched/helped (minimally) a mason in montana build a river rock fireplace, floor to ceiling (cathedral) -- i don't know jack about masonry -- but he used a lot of "L" shaped somewhat corragated metal tabs, seemed like aluminum, flexible behind and then out and under a lot of the stones to "tie" them to the wall. These river stones were collected from the river (Madison) and were bowling ball sized or smaller.

    I stop in to visit the owner whenever i am fishing by his home, and the river rock fireplace is magnificent.
  19. The Dude

    The Dude New Member

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    I just got back from scouting for some local creek stone, and I was able to find a creek that has lots of slab-style sandstone that is thin and flat, similar to what I was picturing. I'd say I can get them to all be 1" or thinner. So I would consider that to be like a veneer. Maybe there is a weight issue still if the natural stone is much heavier than fake stone veneer, I don't know.

    My setup will not be floor to ceiling, but similar to southbalto's that is pictured above. The only difference is that in addition to the rear wall, mine will also be on a side wall. So the weight is doubled, but not doubled on a single wall. One wall is exterior, and I just checked and found out the other wall is directly on top of an I-beam in the basement, running parallel to it. The I-beam runs through the center of the house, and ends of the ceiling joists in the basement overlap and rest on it. To me, these two walls seem to be very well supported from directly below.

    I wasn't planning on slicing any stones through their thickness like I think southbalto explained he did. I can't even imagine the effort and mess involved . I was thinking if the stone was very rounded river rock that split easy, I would try splitting it to get a flat edge for adhesion against the mortar and durock. But the stone I found today is flat and thin already, so I think no cutting or splitting will be required. I did consider cutting grooves with an angle grinder or circular saw for better a better grip, and will most likely be doing that now that it was recommended.

    If anyone has any further doubts like Hogwildz presented, please do share them. his is the reason I asked for advice in the first place. I am not too stubborn or set on absolutely having to see this through to ignore sound advice on any functional possibilities, let alone structural dangers.
  20. southbalto

    southbalto Feeling the Heat

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    Good luck...

    keep us posted on your progress.
  21. begreen

    begreen Mooderator Staff Member

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    I think you're going to do fine. With stone at ~1" thick, this shouldn't be a big challenge. We've seen several hearths done this way here. You want a good bond with the stone and the durock cement board. I would go to the John Bridge forum to inquire about the best bonding mortar. Ask whether to use latex modified thinset or S mortar and other tips.

    http://www.johnbridge.com/
  22. Renovation

    Renovation New Member

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    Thanks for the tip, BG.

    I was going to ask if anyone has any tips on attaching stone to the underside of an angled baffle, like Todd's mason did here:

    http://www.hearth.com/econtent/index.php/forums/viewreply/648868/

    You can see a couple of posts above that one how his mason braced the stone after installing, but I'm wondering how he put it in.

    But I guess I'll take my question there.

    If anyone has any tips or links, I'd appreciate it.
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